Effects of combined alkalinity and ultrasonication on element release and structural alteration in EAF slag

• Electric arc furnace slag was dissolved under different alkaline solutions via ultrasonication and stirring. • Al, Si, Ca, and Fe elements were released depending on alkalinity, technique, and time. • The increasing alkalinity increased Al and Si releases, reaching up to 12% dissolution extents. • Ultrasonication could increase the dissolved Al and Si concentrations up to 50% compared to stirring. This study investigated electric arc furnace (EAF) slag dissolution in varying NaOH solutions (10 M, 0.1 M, and 0.01 M) and assessed the impact of ultrasonication on enhancing element release. After conducting dissolution tests based on 1/100 g/mL as the solid-to-liquid ratio, ICP-OES analysis was used in determining the dissolved elemental concentrations, while XRD, FTIR, BET, and XPS measurements facilitated understanding of the alterations in the structure and surface. According to the findings, Al, Si, Ca, and Fe elements dissolved in different concentrations, depending on the alkalinity level and technique applied. Higher alkalinity led to more Al and Si species dissolving, reaching up to 12 % dissolution. In contrast, moderate and slight alkalinity reduced the extent of dissolution (< 5 %) for Al and Si or even caused the disappearance of some species. Additionally, the results showed that ultrasonication provided more element releases, with up to 50 % enhancement, compared with stirring. XRD patterns revealed that the EAF slag had an intricate crystal structure including more than 15 phases. Use of 10 M NaOH solution resulted in a considerable breakdown of the EAF slag structure and the formation of new phases, whereas the change in structure was less prominent in 0.1 M and 0.01 M NaOH conditions. In another aspect, BET analysis showed that both alkalinity and ultrasonication increased the particle surface area. In conclusion, this study revealed that EAF slag released different elements with various concentrations and NaOH molarities, and ultrasonication was able to enhance the dissolution process to a certain degree.